Two-dimensional folding technique for enhancing Fermi surface signatures in the momentum density: Application to Compton scattering data from an Al-3 at. % Li disordered alloy

We present a technique for enhancing Fermi surface ~FS! signatures in the two-dimensional ~2D! distribution obtained after the 3D momentum density in a crystal is projected along a specific direction in momentum space. These results are useful for investigating fermiology via high-resolution Compton scattering and positron annihilation spectroscopies. We focus on the particular case of the ~110! projection in a fcc crystal where the standard approach based on the use of the Lock-Crisp-West ~LCW! folding theorem fails to give a clear FS image due to the strong overlap with FS images obtained through projection from higher Brillouin zones. We show how these superposed FS images can be disentangled by using a selected set of reciprocal lattice vectors in the folding process. The applicability of our partial folding scheme is illustrated by considering Compton spectra from an Al–3 at. % Li disordered alloy single crystal. For this purpose, high-resolution Compton profiles along nine directions in the ~110! plane were measured. Corresponding highly accurate theoretical profiles in Al–3 at. % Li were computed within the local density approximation ~LDA!–based Korringa-KohnRostoker coherent potential approximation ~KKR-CPA! first-principles framework. A good level of overall accord between theory and experiment is obtained, some expected discrepancies reflecting electron correlation effects notwithstanding, and the partial folding scheme is shown to yield a clear FS image in the ~110! plane in Al–3 at. % Li.